Determining Usable Memory
The MS-DOS command MEM (MEM.COM) provides information about the amount and type of memory available (see Figure 7.13). It provides a quick way to determine how all of the different areas in physical memory are being used and the total amount of RAM actually active on the system.
Figure 7.13 MEM.COM
Most MS-DOS and many early Windows systems load numerous device drivers and TSR (terminate-and-stay resident) programs using the CONFIG.SYS and AUTOEXEC.BAT routines during the boot cycle. These programs are, by default, loaded into conventional memory, taking up valuable space. Memory management techniques are used to load these device drivers and TSRs into the upper memory, allowing more lower memory to be made available to applications.
To determine which device drivers and TSRs are loaded, use the command:
The "/c" is a classify switch. This determines how much conventional memory a certain real-mode program is using (see Figure 7.14).
Figure 7.14 MEM/C
You can also use the Memory button provided with MSD.EXE (Microsoft Diagnostics) to determine the amount and allocation of memory (see Figure 7.15).
Figure 7.15 Microsoft Diagnostics
NOTE
Hexadecimal notation is used by Microsoft Diagnostics. U represents areas of the UMA which are used by TSRs and device drivers.